The Fischer-Tropsch process was developed in the 1920's as a way of producing hydrocarbons from synthesis gas, i.e., hydrogen and carbon monoxide. Initially, the process was centered on producing gasoline range hydrocarbons as automotive fuels. Today, however, the Fischer-Tropsch process is increasingly viewed as a method for preparing heavier hydrocarbons such as diesel fuels, and more preferably waxy molecules for conversion to clean, efficient lubricants. Thus, the importance of catalysts for producing higher boiling hydrocarbons, i.e. a product slate containing a higher carbon number distribution, is ever increasing. A measure of the carbon number distribution is the Schulz-Flory alpha value, which represents the probability of making the next higher carbon number from a given carbon number. The Schulz-Flory distribution is expressed mathematically by the Schulz-Flory equation:Wi=(1−α)2iαi-1Where i represents carbon number, α is the Schulz-Flory distribution factor which represents the ratio of the rate of chain propagation to the rate of chain propagation plus the rate of chain termination, and Wi represents the weight fraction of product of carbon number i. Alpha numbers above about 0.9 are, in general, representative of wax producing processes and the higher the alpha number—as it approaches 1.0—the more selective the process is for producing wax molecules.
The catalysts usually employed in the Fischer-Tropsch process are iron and cobalt; ruthenium has the requisite catalytic activity for use in the process but is expensive and is in relatively short supply. Promoters, like rhenium, zirconium, manganese, and the like, are commonly used, especially with cobalt, to improve various aspects of catalytic performance.
These catalysts are typically supported on a particulate material composed primarily of alumina or titania.
Experience has shown that the operating conditions for Fischer-Tropsch synthesis, especially when conducted in a slurry phase, has led to a weakening of the catalysts and the formation of excessive fines in the reaction mixture. Consequently, efforts have been made to develop improved catalysts.
For example in WO 99/42214 there is disclosed modifying an alumina, titania or magnesia support with a compound selected from compounds of Si, Zr, Cu, Mn, Ba, Co, Zn, Ni or La. In U.S. Pat. No. 6,117,814 an improved support is disclosed which comprises primarily titania in which there is incorporated a binder of silica and alumina.
One object of the present invention is to provide further improved, novel titania supports.
Another object is to provide catalysts supported on such improved titania supports and to use them in the conversion of synthesis gas to achieve high selectivities with low methane formation.